Ester compounds are abundantly found in nature, as well as in medicines, agrochemicals, perfumes, functional materials and the like. In the syntheses of these materials, reactions between corresponding alcohols and carboxylic acids, carboxylic acid chlorides, carboxylic acid anhydrides and the like, or trans-esterification reactions making use of ester compounds are widely used. A series of methods play an important role not only for the purpose of producing ester compounds, but also as a method for protecting a hydroxyl group or a carboxyl group.
A method of using an ester compound derived from a low boiling point alcohol as an acylating agent (transesterification reaction) can be said to be a technique excellent in operability and economic efficiency from the aspect that obtainment (preparation) and handling of the acylating agent are easy, and also that separation of the target product can be carried out in a short step. There have been developed, as the transesterification reaction, classical methods of using a protic acid, as well as many methods of using an aluminum compound, a tin compound or the like as a catalyst. However, these catalysts frequently catalyze not only the intended transesterification reaction, but also undesirable side reactions. Furthermore, when tin compounds are used as catalysts, problems are posed by waste disposal of harmful tin compounds, tin compounds remaining in the products, and the like. An example of the undesirable side reactions may be a decomposition reaction of a functional group that is labile to acid, for example, an alkylideneacetal, a tetrahydropyranyloxy group, a silyloxy group or the like, which are commonly used as protective groups. In addition, racemization which readily undergoes under acidic or basic conditions in the case where there is co-present an asymmetric center, and polymerization reactions in the case where an unsaturated aliphatic group is included, are also included in the undesirable side reactions.
Performing acylation of alcohols each having plural nucleophilic functional groups, as represented by aminoalcohols, in a hydroxyl group-selective manner, is also an important task. A main factor for the occurrence of chemical selectivity in the transesterification reaction may be mentioned as the dependency on the activity of used catalysts, the difference in nucleophilicity of various functional groups, and the stability of produced acyl compounds. For example, Non-Patent Document 1 describes an acylation reaction of aminoalcohols using an aluminum compound as a catalyst, but amide forms in which the amino group is acylated, are obtained as the main resultant product. Furthermore, Non-Patent Document 2 describes an acylation reaction of aminoalcohols in the presence of a carbene catalyst, but amide forms are mainly produced as in the case described above.
Non-Patent Document 1: The Journal of Organic Chemistry 1988, 53, 4172.
Non-Patent Document 2: Organic Letters 2005, 7, 2453.